Keep either the 18-55 or the 28-135 and invest in something on the telephoto end...like a 70-300

This.

Too much overlap with the 18-55mm and 28-135mm. Keeping those two or any one of them with the 15-85mm is just redundant.

Also, keep in mind that when you sell off things on Ebay, they're going to take a huge cut out of your profit. Realistically, I'd look at $400-$450 for a T1i body, $90 for an 18-55mm, and $230 for a 28-135mm.

I'd also consider selling on a forum like POTN instead simply because the buyers there aren't idiots. I've recently sold an FD 50mm f/1.4 on Amazon and the buyer twice tried to get a refund because:

a. Product was "defective" because it wouldn't mount on her 50D
b. Product was "not as advertised" because she assumed it was new even though it clearly was listed as "Used - Good" and she'd have to click on "Used" to even see my listing. x2.

So yea, sell on forums. You'd make the same amount of money more or less anyways (after Ebay/PP fees) and the buyer base is usually more knowledgeable and will give you less headaches, not to mention there's usually less buyer scammers on forums versus Ebay.

And I'd also second the "invest in glass" statement. With regards to bodies, what exactly is your T1i failing at/what does the 60D offer that you need that makes you want to upgrade?

If there really isn't a need there yet, I'd rather just sell off the lenses and go for something else. Personally I'd keep the 28-135mm, sell off the 50mm and 18-55mm for ~$200 total, and spend an extra $200 out of pocket for a used Sigma 30mm f/1.4 or sell off the 28-135mm and 18-55 for ~$330 then spend an extra ~$200 out of pocket for a 70-200 f/4L, and an extra ~$250 out of pocket for a Tamron 17-50 f/2.8 non-VC depending on your needs.

I want to upgrade lenses because the images I get out of my 50MM 1.8 prime lens far surpass the ones I get out of either of my other two lenses. It seems like they are pretty inferior to the better ones like the 15-85, or the L 24-105.